Treatment of impure frying oils

ABSTRACT

Used frying oils are regenerated and made suitable for reuse by treating the used oils with a composition consisting of a mixture of activated clay or magnesium silicate with a gel-derived alumina. The treating composition contains from about 15% by weight to about 75% by weight gel-derived alumina, balance activated clay or magnesium silicate. Treatment with the composition significantly reduces the free fatty acid content of the used oil with simultaneous improvement in color and other important properties thus resulting in a purified oil of substantially extended service life.

This is a division of application Ser. No. 06/896,041, filed Aug. 13,1986, now U.S. Pat. No. 4,701,438.

BACKGROUND OF THE INVENTION

In commercial food processing and particularly in fast food preparationcopious quantities of frying oils and fats are being utilized. Frying offood, such as meat patties, chicken, fish and potatoes, takes place atelevated temperatures and the frying oils and fats, apart from foodresidues, become contaminated with degradation products of the oils andfats. Simple filtration may remove suspended solids, however it does nottake care of dissolved impurities and of the darkened color of the usedoils and fats. The dissolved impurities are generally degradationproducts, such as free fatty acids, aldehydes, ketones, color andodor-forming complex compounds. The presence of these products renderthe frying oils and fats unsuitable for further use and unless the usedoils and fats are purified, health, taste and aesthetic reasons requiretheir disposal.

Several treating agents have been used in the past to purify used oilsand fats. Most of these agents, such as clays, magnesium silicates,zeolites, activated aluminas and charcoal, remove one or more of theimpurities and/or color bodies. However, none of the known treatingagents or composites thereof were found to be fully efficacious for therejuvenation of used frying oils and fats. As a matter of fact, duringtreatment some of the acidic treating agents generate free fatty acids,while others, such as magnesium silicate generate soaps, thus thetreatment itself is associated with the production of undesiredby-products.

It has now been found that a treating composition, consisting of amixture of acid activated clay or magnesium silicate and gel-derivedalumina, accomplishes the desired purification of used frying oils andfats without the disadvantages associated with prior art treatingcompositions.

SUMMARY OF THE INVENTION

Used frying oils and fats are regenerated for renewed use by contactingthe used oils and fats with a treating composition consisting of amixture of activated clay or magnesium silicate and gel-derived alumina.The treating composition contains from about 15% to about 75% by weightgel-derived alumina or magnesium silicate, balance activated clay. Thegel-derived alumina is characterized by a surface rea in the range of280 to 350 m² /g, a pseudoboehmite content of at least 20% by weight anda loss on ignition (LOI) in the range of 24 to 32% by weight. Theactivated clay is an acid activated bentonite. The magnesium silicateutilized in the present invention is characterized by a nominalstructure of 2MgO:5SiO₂ (the ratio of MgO:SiO₂ can vary) and it can befound in nature (talc, serpentine) or synthetized by the interaction ofa magnesium salt and a soluble silicate. The surface area of suitablemagnesium silicates is generally in the range from 400 to 500 m² /g andit exhibits a loss on ignition (1 hour at 1000° C.) of about 20-30% byweight.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to the purification of used frying oils and fatsby treatment with a clay-alumina or magnesium silicate-aluminacomposition. More particularly, it concerns the removal of degradationproducts and color bodies from used frying oils and fats by treatingthese oils and fats with a composition containing gel-derived,pseudoboehmitic alumina and activated clay or magnesium silicate.

For the purposes of this invention the term "frying oils and fats" referto those animal and vegetable derived oils and fats which arecustomarily used in frying foods. These oils and fats are generallymixtures of mixed glycerides and include both saturated and unsaturatedcompounds and mixtures thereof. Typical oils and fats employed in thefood industry include animal fats, lard and tallow; olive, peanut, corn,soybean, sunflower, safflower and fish oils. The major constituents inthese oils and fats are esterified oleic and linoleic acids. Mixtures ofoils and fats are also included within the meaning of the abovedefinition.

"Activated clay" as used herein refers to bentonite clay activated withan acid, such as sulfuric acid, to remove acid-soluble constituents andimpurities. The acid-treated clay is washed, dried and ground. Typicalactivated bentonite clay exhibits a surface area in the range of 275 m²/g to 325 m² /g; an acidity in the range of 3 to 12, expressed inmgKOH/g clay required for neutralization of an aqueous clay slurrycontaining 16.6 grams clay per liter of water; a particle size whereinat least 40% by weight of the particles pass through a screen havingopenings of 0.074 mm.

The expression "magnesium silicate" as referred to herein means anaturally occurring or synthetic hydrated magnesium silicate having anominal composition of 2MgO:5SiO₂ xH₂ O, a surface area in the rangefrom about 400 to about 500 m² /g, a loss on ignition, measured afterheat treatment for 1 hour at 1000° C., from about 20 to about 30% byweight, a particle size, wherein from about 40 to about 70% by weight ofthe particles pass through a screen having openings of 0.074 mm.

The terms "gel-derived" or "pseudoboehmitic" alumina, as used hereinrelates to an alumina prepared by either (a): reacting a basic aluminumsalt, such as sodium aluminate, with an acid or acidic aluminum saltsolution, for example a mineral acid or an aqueous solution of Al₂(SO₄)₃, AlCl₃ or Al(NO₃); or (b): by reacting an acidic aluminum saltsolution with a base, such as NaOH. The alumina suitable for being usedin the treating composition of the present invention is characterized bya pseudoboehmite content of at least 20% by weight as determined byX-ray diffraction using copper Kα-radiation as described in U.S. Pat.No. 3,630,670. The alumina is further characterized by a surface area inthe range of about 280 to about 350 m² /g, a bulk density in the rangeof about 10-16 lbs/ft³ (160-260 kg/m³) and a loss on ignition (whenheated to 1000° C. for 1 hour) in the range of about 24-32% by weight.The particle size of the gel-derived alumina employed is small, not lessthan 60% by weight passes through a screen having openings of 0.074 mm.

The treating composition employed for the purification of the usedfrying oils and fats contains from about 15% to about 75% by weightgel-derived alumina, balance activated clay or magnesium silicate.Preferably, the composition contains from about 30% to about 50% byweight gel-derived alumina, balance activated clay or magnesiumsilicate. The components are carefully admixed in order to obtain amixture of substantial uniformity. To avoid segregation of theconstituents of the treating composition, the particle size distributionof the individual components, i.e. the magnesium silicate or activatedclay and alumina, is kept reasonably uniform. Preferably, the percentageof particles having a particle size below about 0.044 mm is minimized inorder to avoid problems in the treatment step.

Treatment of the used frying oils or fats with the treating compositionis usually accomplished by contacting the used oils or fats with thetreating composition at temperatures above the solidificationtemperature of the oils or fats. Preferably, the temperature of theliquid oils or fats to be purified is within the temperature range fromabout 120° C. to about 190° C. Lower temperatures affect the efficiencyof the treatment, while higher temperatures may cause the oils or fatsto further degrade, thus causing losses.

Contacting of the liquid oils and fats can be accomplished according toconventional methods. For example, the treating composition can beuniformly dispersed in the oil or fat to be purified and kept dispersedduring the treatment by agitation. After the treatment is finished thepurified oil or fat can be separated from the spent treating agent byfiltration, centrifuging or decantation. It is also possible to conductthe hot oils or fats through a filter cartridge filled with the treatingagent.

The quantity of treatment agent utilized per weight unit of used oil orfat depends on the degree of contamination of the oils or fats to betreated. It has been found that acceptable purification can be achievedin terms of color improvement, free fatty acid and soap removal, andpolar body elimination when the weight of treating agent to oil or fatis kept in the range from about 1% to 10%, preferably 1.5-3% by weight.Higher ratios naturally improve the effectiveness, the balancing factorto be taken into consideration is the ease and rate by which thepurified oils and fats can be separated from the spent treating agent.Treatment times depend on the manner of treatment, the temperature ofthe oils and fats to be treated, the ratio of treating agent to thematerial to be treated, the type of oils and fats treated and the degreeof contamination of the used fats and oils. Consequently, no settreating times can be given which would apply under all circumstances.It can however be stated, that under the usual treatment conditions,i.e. using the treatment temperature range set out above and the minimumtreatment agent to used oil or fat weight ratio referred to before,treatment times as short as 3 minutes were found to result insatisfactory purification when the treating agent was substantiallyuniformly dispersed within the used oil or fat.

Subsequent to the treatment with the novel treating composition andafter separation of the spent treating agent, the treated and purifiedoil or fat is ready for reuse. The spent treating agent is generallydiscarded. If desired, fresh unused oil or fat may be added to thepurified oil or fat. This addition generally lengthens the service lifeof the oil or fat and allows multiple regenerations or rejuvenationsafter repeated use.

The following Examples will further illustrate the effectiveness of thenovel treating composition for purifying used frying oils and fats.

EXAMPLE I

Tallow/cottonseed oil-based frying medium, used for deep frying ofbreaded chicken pieces and containing as a result of oxidativedegradation color bodies, free fatty acids, soaps and polar compoundswas subjected to purification. The used frying medium was kept at atemperature of about 177° C. and 60 g of treating agent containing 45%by weight of gel-derived lumina, balance activated clay, was added toeach kg of used oil. The treating agent was thoroughly dispersed in theused frying medium and the contact between the frying medium and thetreating agent was kept for 5 minutes under agitation. Subsequently, thesuspended solids were removed by filtration. The purified frying mediumwas then analyzed for color, free fatty acid, soap and polar compoundcontent. The purification test was repeated using under the same testingconditions the following materials for purification: activated bentoniteclay, gel-derived alumina, magnesium silicate and diatomaceous earth.The results were tabulated and are shown in Table I.

                                      TABLE I                                     __________________________________________________________________________    Comparison of the Purification Effectiveness of                               Different Treating Materials on Used Frying Medium.                           TALLOW/COTTONSEED-BASED FRYING OIL                                                                 FREE        POLAR BODY                                   TREATING  COLOR      FATTY ACID                                                                            SOAP                                                                              CONTENT                                      MATERIAL  (LOVIBOND-RED)                                                                           % BY WT.                                                                              ppm FOS No..sup.(1)                              __________________________________________________________________________    Gel-derived alumina                                                                     2.8        2.41    0   3.28                                         activated bentonite                                                           Gel-derived alumina                                                                     3.2        1.85    4   3.48                                         Activated bentonite                                                                     2.1        3.45    0   3.01                                         Magnesium silicate                                                                      2.9        2.37    107 3.32                                         Untreated 3.5        2.92    67  3.65                                         __________________________________________________________________________     .sup.(1) Polar body content (FOS number) was determined by using a "Food      Oil Sensor", available from Northern Instrument Corporation. The              instrument measures relative dielectric constants for oils and the            dielectric constants are correlated wit h the weight percent polar            material in the oils.                                                    

EXAMPLE II

Tallow/cottonseed frying medium was employed for frying breaded chickenpieces. The used frying medium, containing color bodies, free fattyacids, soaps and polar compounds, was subjected to purification using agel-derived alumina-clay composition, containing 25% by weightgel-derived alumina, balance activated bentonite. The treatment wasaccomplished at about 177° C. by contacting the impure frying medium forabout 5 minutes with the treating composition under agitation. Thequantity of treating composition utilized was about 6% by weight of thefrying medium. The tests were repeated with fresh samples of impurefrying oil using 35:65 and also 50:50 mixtures of gel-derivedalumina-activated bentonite compositions. Comparison tests were also runwith: gel-derived alumina, activated bentonite, magnesium silicate,diatomaceous earth and activated carbon. The results are shown in TableII.

                                      TABLE II                                    __________________________________________________________________________    Comparison of the Purification Effectiveness of                               Different Treating Materials on Used Frying Medium.                           TALLOW-COTTONSEED FRYING OIL                                                                       FREE         POLAR BODY                                  TREATING  COLOR      FATTY ACID                                                                            SOAP CONTENT                                     MATERIAL  (LOVIBOND-RED)                                                                           % BY WT.                                                                              ppm  FOS No.                                     __________________________________________________________________________    Gel-derived alumina                                                                     1.78       3.47    0    3.73                                        activated bentonite                                                           (25%:75% mixture)                                                             Gel-derived alumina                                                                     1.78       3.33    0    3.83                                        +                                                                             activated bentonite                                                           (35%:65% mixture)                                                             Gel-derived alumina                                                                     1.80       3.17    0    3.88                                        +                                                                             activated bentonite                                                           (50%:50% mixture)                                                             Gel-derived alumina                                                                     1.90       2.62    0    4.00                                        Activated bentonite                                                                     1.65       4.57    0    3.37                                        Magnesium silicate                                                                      1.98       3.53    1500 4.02                                        Diatomaceous earth                                                                      2.10       3.78    92   4.39                                        Activated carbon                                                                        1.92       3.47    55   4.17                                        Untreated 2.00       3.79    22   4.15                                        __________________________________________________________________________

EXAMPLE III

The purification test was repeated with a used vegetable frying oilwhich was utilized for frying multiple products, such as chicken,potatoes, fish and taco shells. Purification was accomplished under thesame treatment conditions described in Example II. The purificationresults were tabulated and are shown in Table III.

                                      TABLE III                                   __________________________________________________________________________    Comparison of the Purification Effectiveness of                               Different Treating Materials on Used Frying Medium.                           VEGETABLE FRYING OIL                                                                               FREE         POLAR BODY                                  TREATING  COLOR      FATTY ACID                                                                            SOAP CONTENT                                     MATERIAL  (LOVIBOND-RED)                                                                           % BY WT.                                                                              ppm  FOS No.                                     __________________________________________________________________________    Gel-derived alumina                                                                     1.70       3.85    0    0.74                                        activated bentonite                                                           (25%:75% mixture)                                                             Gel-derived alumina                                                                     1.78       3.74    0    0.75                                        +                                                                             activated bentonite                                                           (35%:65% mixture)                                                             Gel-derived alumina                                                                     1.88       3.60    0    0.79                                        +                                                                             activated bentonite                                                           (50%:50% mixture)                                                             Gel-derived alumina                                                                     2.42       2.94    0    0.92                                        Activated bentonite                                                                     0.98       4.58    0    0.57                                        Magnesim silicate                                                                       2.58       3.95    1680 0.97                                        Diatomaceous earth                                                                      2.88       4.25    94   1.13                                        Untreated 2.70       4.27    20   1.08                                        __________________________________________________________________________

EXAMPLE IV

The purification test was repeated by treating a tallow-cottonseedshortening, which was previously used for frying breaded chicken pieces,with magnesium silicate--gel alumina mixtures. The treatment wasaccomplished at about 177° C. and the used shortening was contacted forabout 5 minutes with about 6% by weight magnesium silicate--gel aluminamixture. For comparison purposes, individual magnesium silicate andgel-derived alumina were also used for purification. The results weretabulated and are shown in Table IV.

                  TABLE IV                                                        ______________________________________                                        Purification of Used Shortening                                                           Color                                                                         (Lovi-                   Polar Body                                           bond    Free Fatty Soap  Content                                  Treating Material                                                                         Red)    Acid (Wt. %)                                                                             ppm   (FOS No.)                                ______________________________________                                        30% Gel-derived                                                                           2.78    3.68       32    3.44                                     alumina                                                                       70% Mag. silicate                                                             35% Gel-derived                                                                           2.78    3.64       23    3.44                                     alumina                                                                       65% Mag. silicate                                                             40% Gel-derived                                                                           2.80    3.59       24    3.48                                     alumina                                                                       60% Mag. silicate                                                             50% Gel-derived                                                                           2.82    3.56       14    3.49                                     alumina                                                                       50% Mag. silicate                                                             Magnesium silicate                                                                        2.70    3.84       141   3.31                                     Gel-derived alumina                                                                       3.02    3.32       2     3.56                                     Untreated oil                                                                             3.25    4.57       34    3.69                                     ______________________________________                                    

From the results shown in the Examples it becomes clear that thegel-derived alumina-activated bentonite or magnesium silicate treatingcompositions provide an overall improved purification efficiency incomparison to the individual components and also in comparison to priorart purification agents.

It is apparent from the description and the examples that variouschanges and modifications may be made to the invention without departingfrom the spirit thereof. Accordingly, the scope of the invention is onlylimited by the appended claims.

What is claimed is:
 1. A process for removing undesired impuritiesincluding color bodies from impure frying oils and fats which comprisescontacting the impure oils and fats at a temperature in the range fromabout 120° C. to about 190° C. with a treating composition consisting ofa mixture of gel-derived alumina and acid activated bentonite ormagnesium silicate, the mixture containing from about 15 to about 75% byweight, gel-derived alumina, the balance being acid activated bentoniteor magnesium silicate, the quantity of the composition being used forthe treatment being in the range from about 1 to about 10% by weight ofthe oil or fat being treated, maintaining the contact for a timesufficient to remove at least a portion of the undesired impurities,including color bodies, separating the treating composition from the oilor fat and recovering a purified oil or fat of substantially reducedimpurity content and of improved color.
 2. Process according to claim 1,wherein the mixture contains from about 30 to about 50% by weight ofgel-derived alumina.
 3. Process according to claim 1, wherein thequantity of the mixture used for the treatment is from about 3 to about6% by weight of the oil or fat to be treated.
 4. Process according toclaim 1, including uniformly dispersing the treating composition in theoil or fat and separating the composition from the oil or fat byfiltration.